Films made of a syndiotactic polystyrene resin composition are films excellent in the heat resistance, chemical resistance, hot water resistance, dielectric characteristics, electrical insulation property and the like. Thus, syndiotactic polystyrene films are expected to be used in various applications. In particular, since the films are excellent in the dielectric characteristics and have high electrical insulation property and heat resistance, they are expected to be used as insulators for capacitors (Patent Documents 1 and 2). In addition, the films have been further improved, and for example, Patent Document 3 discloses a technique for increasing the withstand voltage by preventing impurities in a film. Patent Document 4 discloses a technique for improving the handling property and wear resistance by adjusting the added particles and the like. Patent Documents 5 and 6 disclose a technique for reducing the thickness variation by adjusting the refractive index of a film. Further, in these Patent Documents 3 to 6, the techniques are all disclosed as techniques regarding syndiotactic polystyrene films used for capacitor applications. In addition, Patent Document 7 discloses a technique for increasing the breakdown voltage by adding an antioxidant.
The syndiotactic polystyrene films disclosed in Patent Documents 1 to 6 are used as insulators for capacitors. However, for higher performance capacitors, such as capacitors installed in the recent hybrid cars, for example, films that are more excellent in the electrical characteristics such as the breakdown voltage and the heat resistance are required, and the properties are sometimes not sufficient. In addition, although the syndiotactic polystyrene film disclosed in Patent Document 7 is suitably used for a capacitor for a hybrid car and the like, further improvement of the heat resistance and the breakdown voltage is required.    Patent Document 1: JP-A-1-182346 publication    Patent Document 2: JP-A-1-316246 publication    Patent Document 3: JP-A-3-124750 publication    Patent Document 4: JP-A-6-80793 publication    Patent Document 5: JP-A-7-156263 publication    Patent Document 6: JP-A-8-283496 publication    Patent Document 7: JP-A-2009-235321 publication